Cardiac rhythm management devices can include implantable or ambulatory devices, such as pacemakers, cardioverter defibrillators, and/or devices that can monitor one or more physiological parameters, and/or provide one or a combination of pacing, defibrillation, or cardiac resynchronization therapies. Such devices can be configured for use with a plurality of implanted or external electrodes, such as to detect and/or treat cardiac conditions. These electrodes may be configured in a plurality of different combinations for sensing cardiac electrical activity and/or delivering electrical stimulation therapy. Using different combinations of electrodes for sensing cardiac electrical activity may result in differing results for different electrode combinations for sensed electrical activity of a same cardiac cycle. Using different combinations of electrodes for delivering electrical stimulation therapy to the heart may similarly result in differing effectiveness of the therapy. Each of these electrode configurations may be termed a “vector.” Selecting a proper vector for sensing cardiac electrical activity and/or for delivering electrical stimulation therapy can help improve treatment.